Dabius pabkhubst



(No Model.)

D. PARKHURST. HEAD BLOCK PoR' SAW MILLS.

1\T0.267","923x Patented Nov. 21, 1882.

fnvelon: i 'M/M9 @MM UNITED STATES DAEIUs PARKHUEST, `E sT'. LOUIS,

MISSOURI, ASSIGNOR OF ONE-HALF TO GEORGE H. KNIGHT, OF SAME PLAGE.

HEAD-BLOCK Fon SAW-MILLS.

SPECIFICATIO'N forming part of Letters Patent No. 267,923, dated November 21, 1882.

Application filed August 2, 1882. (No model.)

To all whom it may concern:

Beit known that I, DARIUs PARKIIURST, of

. the city of St. L ouis, in the State'of Missouri,

have invented a certain new and useful Improvement in FrictionBrakes for Saw-Mill Head-Blocks, of which the following is a full, clear, and exact description, reference being had to the accompanying drawings, forming part of this specication, and in which- Figure l is a side elevation Fig. 2, a detail side View, and Fig. 3 an enlarged detail perspective View.

The present invention relates to an improvement on Letters Patent No. 257,060, granted to myself and assignee, April 25,1882; and it consists in a device to prevent any possibility of the main wheel turning backward when at Work, but not interfering with its free forward movement, as more fullyset forth hereinafter. Referring to the drawings, A represents the frame; B, .the combined index, ratchet, and brake-wheel; O, the index-arm D, the operating-lever; E, the reversible pawl; F, the strap-brake; G, the brake-lever, and H H the standards to which the brake-lever ispivoted. All these parts are fully shown and described inthe patent referred to, and therefore need no i'urther`description, either as to their for mation or operation, here.

lIn practice it has been found that when both the operating-lever and the index-arm are brought back at the same time, when the machine is at Work, the pressure of the pawl against the ratchet-wheel as it slips over the teeth is liable to cause a slight backward movement of the wheel, which would prevent the index engaging the proper notch. As before stated, this difficulty is onlyliable to occur when both the index-and the lever are brought back at the same time, for if the lever l is brought back first, while the index is still vengaging the notch I of the arm J., the wheel cannot possibly turn, for, as stated in the said former patent, the index engages this notch I and the wheel at the same time. It lwas at first proposed to prevent this liability of the wheel turning back by slightly applying the strapbrake, and the only objection to this manner of meeting the difficulty is that a slight pressure is upon the wheel continually, not only when the index and lever are brought back,

Now, to prevent any liability of the wheel turningwhen the lever and index are thus brought back together, and at the same time not have any unnecessary friction when the wheel is moved forward, is `the object of the present invention; .and it is accomplished. by pivoting to the'upper ends of the standards H a f'riction-bloclQL, which can be thrown over into engagement with the face of the wheel, as shown, or thrown back out of engagement therewith. As it is a less distance from the pivot to the face of the wheel than from the pivot tothe part of the block that bears against the wheel, it will be seen that when the block is againstthe wheel it will be impossible for the latter to turn back, while its free forward movement is not in the least interfered with.

I claim- In a saw-mill head-block, the combination of combined index, ratchet, and brake-wheel B, with horizontal frame A, standards H H, formed on said frame, and friction block L, hinged between said standards, as set forth.

DAEIUs PAEKHURST.

but also when the wheel is turning forward. 

